Adsorption and removal studies of cadmium ion onto sulfonic/phosphonic acid functionalization resins

Removal of cadmium and lead ions from aqueous solutions by novel dolomite-quartz@Fe3O4 nanocomposite fabricated as nanoadsorbent

The elimination of heavy metal ion contaminants from residual waters is critical to protect humans and the environment. The natural clay (dolomite and quartz) based composite Fe₃O₄ nanoparticles (DQ@Fe₃O₄) has been largely explored for this purpose. Experimental variables such as temperature, pH, heavy metal concentration, DQ@Fe₃O₄ dose, and contact time were optimized in details. The DQ@Fe₃O₄ nanocomposite was found to achieve maximum removals of 95.02% for Pb²⁺ and 86.89% for Cd²⁺, at optimal conditions: pH = 8.5, adsorbent dose = 2.8 g L^-1, the temperature = 25 °C, and contact time = 140 min, for 150 mg L^-1 heavy metal ion initial concentration. The Co-precipitation of dolomite-quartz by Fe₃O₄ nanoparticles was evidenced by SEM-EDS, TEM, AFM, FTIR, XRD, and TGA analyses. Further, the comparison to the theoretical predictions, of the adsorption kinetics, and at the equilibrium, of the composite, revealed that they fit, respectively to, the pseudo-second-order kinetic, and Langmuir isotherm. These both models were found to better describe the metal binding onto the DQ@Fe₃O₄ surface. This suggested a homogenous monolayer sorption dominated by surface complexation. Additionally, thermodynamic data have shown that the adsorption of heavy metal ions is considered a spontaneous and exothermic process. Moreover, Monte Carlo (MC) simulations were performed in order to elucidate the interactions occurring between the heavy metal ions and the DQ@Fe₃O₄ nanocomposite surface. A good correlation was found between the simulated and the experimental data. Moreover, based on the negative values of the adsorption energy (Eads), the adsorption process was confirmed to be spontaneous. In summary, the as-prepared DQ@Fe₃O₄ can be considered a low-cost-effective heavy metals adsorbent, and it has a great potential application for wastewater treatment.

Characterization and Optimization of Polymeric Bispicolamine Chelating Resin: Performance Evaluation via RSM Using Copper in Acid Liquors as a Model Substrate through Ion Exchange Method

Advanced technologies of electronics industries have led to environmental contamination concerns, especially waste print circuit boards containing a very high concentration of copper (II) ions, which can be discharged in wastewater containing many contaminated metals. A low pH is a necessity for treating industrial wastewater containing heavy metals to meet engineering process design. A novel polymeric bispicolamine chelating resin, Dowex-M4195, was applied as an alternative for investigating the behavior of copper (II) in acidic solution via an ion exchange method in a batch experiment system. Characterization of physical and chemical properties before and after ion exchange were also explored through BET, SEM-EDX, FTIR and XRD. Response surface methodology was also applied for optimization of copper (II) removal capacity using design of experiment for selective chelating resin at a low pH. The results indicate that H+ Dowex-M4195 chelating resin had a high-carbon content and specific surface area of >64% and 26.5060 m2/g, respectively. It was predominantly macropore porous in nature due to the N2 gas adsorption isotherm and exhibited type IV with insignificant desorption hysteresis loop of H1-type. It was spherical and cylindrical. After the ion exchange process of copper (II)-loaded H+ Dowex-M4195, the specific surface area and total pore volume decreased by about 17.82% and 5.39%, respectively, as compared to H+ Dowex-M4195. Hysteresis loop, isotherm and pore size distribution were also similar. Regarding the functional group, the surface morphology and crystalline structures of H+ Dowex-M4195 showed copper (II) compound based on the structure of chelating resin that confirmed effective ion exchange behavior. The design of optimization indicated that copper (II) removal capacity of about 31.33 mg/g was achieved, which could be obtained at 6.96 h, pH of 2 (a desirable low pH), dose of 124.13 mg and concentration of 525.15 mg/L. The study indicated that the H+ Dowex-M4195 (which is commercially available on the market) can successfully be applied as an alternative precursor through the ion exchange method for further reuse and regeneration of the copper (II) in the electronic waste industries and other wastewater applications needed to respond the policy of biocircular green economy in Thailand.